"Automatic splices" are used to longitudinally splice two lengths of cable together. Such devices are typically used by power utility linemen to splice lengths of high voltage cable together.
U.S. Pat. No. 3,205,300 issued 7 September, 1965 to Becker for a "Cable Gripping Unit" is typical of the prior art. The opposed ends of Becker's device each contain a set of tapered jaws. The lineman inserts the cable ends through apertures provided in each of the opposed ends of the device. After inserting suitable lengths of each cable into the device, the lineman draws the cables longitudinally away from the device. This action pulls the jaws into the tapered ends of the device's casing, thereby securely clamping the jaws on to the cable.
During cable insertion into prior art splicing devices, the lineman must feed the cable through the jaws. But, the jaws are pressed into the tapered casing by the action of a spring, and are not held open to allow unimpeded insertion of the cable. The inside of the jaws have serrated teeth which tend to resist cable insertion. To aid cable insertion, prior art devices provide a cup on the inside of each aperture. The cup covers the cut end of the cable as it is advanced through the jaws, to help prevent the serrated jaw teeth from catching on the cable end.
In practice, lineman have had some difficulty installing prior art splicing devices because the cable end, despite the aforesaid cup, sometimes gets caught in the jaws. Since there is no positive indication that the cable end has been fully inserted through the jaws, the lineman may leave the cable inserted only partly through the jaws. This is undesirable, because the mechanical contact between the jaws and the cable may be insufficient for long term retention of the cable and because the electrical conduction characteristics of the device may be impaired if only part of the jaws contact the cable. Although the lineman is typically instructed to mark the cable to indicate its full insertion length, in fact this is seldom done. There have been many cases in which improperly installed splices have allowed high voltage cables to fall to the ground.
The present invention overcomes the foregoing problems by providing a spring-loaded mechanism which initially holds the jaws well away from the cable, allowing free advancement or retraction of the cable relative to the jaws until the device is activated to clamp the jaws on to the cable. The invention does not require cups to cover the cable ends since the jaws are held well away from the cable. The invention also provides a positive indication that the cable end has been fully inserted through the jaws. The lineman need not mark the cable to indicate full insertion length.
An additional problem with prior art splicing devices is that they can only be used for splicing cables which are under high mechanical tension. This is because the higher the cable tension, the further the tapered jaws are pulled into the tapered casing and the tighter the cable is gripped. High cable tension also provides a large force to press the jaws against the casing and thus give good electrical contact. When prior art splices are used on short cable spans with very light mechanical loads, electrical connection is poor and overheating may result. In the present invention the spring can be made sufficiently powerful to press the jaws firmly into the tapered casing. It is therefore not necessary to rely solely on cable mechanical tension to provide a high applied force between the jaws and casing. A powerful spring cannot be used in prior art splices since it would aggravate the problem of feeding the cable through the jaws during installation. In the present invention, the jaws are held open during cable insertion and the spring may therefore be sufficiently strong to allow the device to be used with low cable tension.